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1.
Sara J. Palmer J. Kristóf Veronika Vágvölgyi Erzsébet Horváth R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,96(2):449-454
The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg6Al2(OH)16[Fe(CN)6]0.5·7H2O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg6Al2(OH)16[Fe(CN)6]0.66·9H2O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite. 相似文献
2.
Intercalation of hydrotalcites with hexacyanoferrate(II) and (III)—a thermoRaman spectroscopic study
Ray L. Frost Anthony W. Musumeci Jocelyn Bouzaid Moses O. Adebajo Wayde N. Martens J. Theo Kloprogge 《Journal of solid state chemistry》2005,178(6):1940-1948
Raman spectroscopy using a hot stage indicates that the intercalation of hexacyanoferrate(II) and (III) in the interlayer space of a Mg, Al hydrotalcites leads to layered solids where the intercalated species is both hexacyanoferrate(II) and (III). Raman spectroscopy shows that depending on the oxidation state of the initial hexacyanoferrate partial oxidation and reduction takes place upon intercalation. For the hexacyanoferrate(III) some partial reduction occurs during synthesis. The symmetry of the hexacyanoferrate decreases from Oh existing for the free anions to D3d in the hexacyanoferrate interlayered hydrotalcite complexes. Hot stage Raman spectroscopy reveals the oxidation of the hexacyanoferrate(II) to hexacyanoferrate(III) in the hydrotalcite interlayer with the removal of the cyanide anions above 250 °C. Thermal treatment causes the loss of CN ions through the observation of a band at 2080 cm−1. The hexacyanoferrate (III) interlayered Mg, Al hydrotalcites decomposes above 150 °C. 相似文献
3.
Ray L. Frost Anthony W. Musumeci Thor Bostrom Moses O. Adebajo Matt L. Weier Wayde Martens 《Thermochimica Acta》2005,429(2):179-187
The thermal decomposition of hydrotalcites with chromate, molybdate and sulphate in the interlayer has been studied using thermogravimetric analysis coupled to a mass spectrometer measuring the gas evolution. X-ray diffraction shows the hydrotalcites have a d(0 0 3) spacing of 7.98 Å with very small differences in the d-spacing between the three hydrotalcites. XRD was also used to determine the products of the thermal decomposition. For the sulphate-hydrotalcite decomposition the products were MgO and a spinel MgAl2O4, for the chromate interlayered hydrotalcite MgO, Cr2O3 and spinel. For the molybdate interlayered hydrotalcite the products were MgO, spinel and MgMoO4. EDX analyses enabled the formula of the hydrotalcites to be determined. Two processes are observed in the thermal decomposition namely dehydration and dehydroxylation and for the case of the sulphate interlayered hydrotalcite, a third process is the loss of sulphate. Both the dehydration and dehydroxylation take place in three steps each for each of the hydrotalcites. 相似文献
4.
R. L. Frost A. W. Musumeci M. O. Adebajo W. Martens 《Journal of Thermal Analysis and Calorimetry》2007,89(1):95-99
Hydrotalcites of formula Mg6A12(OH)16(PO4)·4H2O formed by intercalation with the phosphate anion as a function of pH show variation in the d-spacing attributed to the size of the hydrated anion in the interlayer. The value changes from 11.91 Å for pH 9.3, to 7.88 Å at pH 12.5. No crystalline hydrotalcites with phosphate in the interlayer were formed at pH 9.3. Thermal decomposition identifies three steps namely dehydration, dehydroxylation and some loss of carbonate during the thermal treatment. The addition of a thermally activated ZnAl-HT to a phosphate solution resulted in the uptake of the phosphate and the reformation of the hydrotalcite. The technology has the potential for water purification through anion removal. 相似文献
5.
Sara J. Palmer R. L. Frost T. Nguyen 《Journal of Thermal Analysis and Calorimetry》2008,92(3):879-886
Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were
characterized by XRD, and TG/DTA to determine the stability of the hydrotalcites synthesized. The thermal decomposition of
carbonate hydrotalcites consist of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation
and decarbonation of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where
the first step is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting
with the interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding
metal oxides, including MgO, Al2O3, MgAl2O4, NaMg4(VO4)3 and Na2Mg4(MoO4)5. The presence of oxy-anions proved to be beneficial in the stability of the hydrotalcite structure, shown by the delay in
dehydroxylation of oxy-anion containing hydrotalcites compared to the carbonate hydrotalcite. This is due to the substantial
amount of hydroxyl groups involved in a network of hydrogen bonds involving the intercalated anions. Therefore, the stability
of the hydrotalcite structure appears to be dependent on the type of anion present in the interlayer. The order of thermal
stability for the synthesized hydrotalcites in this study is Syn-HT-V>Syn-HT-Mo> Syn-HT-CO3-V>Syn-HT-CO3-Mo>Syn-HT-CO3. Carbonate containing hydrotalcites prove to be less stable than oxy-anion only hydrotalcites. 相似文献
6.
N. Voyer A. Soisnard Sara J. Palmer W. N. Martens R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,96(2):481-485
Zn-Al hydrotalcites and Cu-Al hydrotalcites were synthesised by coprecipitation method and analysed by X-ray diffraction (XRD)
and thermal analysis coupled with mass spectroscopy. These methods provide a measure of the thermal stability of the hydrotalcite.
The XRD patterns demonstrate similar patterns to that of the reference patterns but present impurities attributed to Zn(OH)2 and Cu(OH)2. The analysis shows that the d003 peak for the Zn-Al hydrotalcite gives a spacing in the interlayer of 7.59 ? and the estimation
of the particle size by using the Debye-Scherrer equation and the width of the d003 peak is 590 ?. In the case of the Cu-Al
hydrotalcite, the d003 spacing is 7.57 ? and the size of the diffracting particles was determined to be 225 ?.
The thermal decomposition steps can be broken down into 4 sections for both of these hydrotalcites. The first step decomposition
below 100°C is caused by the dehydration of some water absorbed. The second stage shows two major steps attributed to the
dehydroxylation of the hydrotalcite. In the next stage, the gas CO2 is liberated over a temperature range of 150°C. The last reactions occur over 400°C and involved CO2 evolution in the decomposition of the compounds produced during the dehydroxylation of the hydrotalcite. 相似文献
7.
A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of synthetic hydrotalcites reevesite (Ni6Fe2(CO3)(OH)16·4H2O) and pyroaurite (Mg6Fe2(SO4,CO3)(OH)16·4H2O) and the cationic mixtures of the two minerals. XRD patterns show the hydrotalcites are layered structures with interspacing distances of around 8.0. Å. A linear relationship is observed for the d(001) spacing as Ni is replaced by Mg in the progression from reevesite to pyroaurite. The significance of this result means the interlayer spacing in these hydrotalcites is cation dependent. High resolution thermal analysis shows the decomposition takes place in 3 steps. A mechanism for the thermal decomposition is proposed based upon the loss of water, hydroxyl units, oxygen and carbon dioxide. 相似文献
8.
Bayer hydrotalcites prepared using the seawater neutralisation (SWN) process of Bayer liquors are characterised using X-ray diffraction and thermal analysis techniques. The Bayer hydrotalcites are synthesised at four different temperatures (0, 25, 55, and 75 °C) to determine the effect of synthesis temperature on the thermal stability of the Bayer hydrotalcite structures and the mineralogical phases that form. The interlayer distance increased with increasing synthesis temperature, up to 55 °C, and then decreased by 0.14 Å for Bayer hydrotalcites prepared at 75 °C. The three mineralogical phases identified in this investigation are; (1) Bayer hydrotalcite, (2), calcium carbonate species, and (3) hydromagnesite. The DTG curve can be separated into four decomposition steps; (1) the removal of adsorbed water and free interlayer water in hydrotalcite (30–230 °C), (2) the dehydroxylation of hydrotalcite and the decarbonation of hydrotalcite (250–400 °C), (3) the decarbonation of hydromagnesite (400–550 °C), and (4) the decarbonation of aragonite (550–650 °C). 相似文献
9.
Sara J. Palmer H. J. Spratt R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,95(1):123-129
Thermal analysis complimented with evolved gas mass spectrometry has been applied to hydrotalcites containing carbonate prepared
by coprecipitation and with varying divalent/trivalent cation ratios. The resulting materials were characterised by XRD, and
TG/DTG to determine the stability of the hydrotalcites synthesised. Hydrotalcites of formula Mg4(Fe,Al)2(OH)12(CO3)·4H2O, Mg6(Fe,Al)2(OH)16(CO3)·5H2O, and Mg8(Fe,Al)2(OH)20(CO3)·8H2O were formed by intercalation with the carbonate anion as a function of the divalent/trivalent cationic ratio.
XRD showed slight variations in the d-spacing between the hydrotalcites. The thermal decomposition of carbonate hydrotalcites
consists of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation and decarbonation
of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where the first step
is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting with the
interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding metal
oxides and spinels, including MgO, MgAl2O4, and MgFeAlO4. 相似文献
10.
Ray L. Frost Sara J. Palmer Laure-Marie Grand 《Journal of Thermal Analysis and Calorimetry》2010,101(3):859-863
Insight into the unique structure of layered double hydroxides (LDHs) has been obtained using a combination of X-ray diffraction and thermal analysis. Indium containing hydrotalcites of formula Mg4In2(CO3)(OH)12·4H2O (2:1 In-LDH) through to Mg8In2(CO3)(OH)18·4H2O (4:1 In-LDH) with variation in the Mg:In ratio have been successfully synthesised. The d(003) spacing varied from 7.83 Å for the 2:1 LDH to 8.15 Å for the 3:1 indium containing LDH. Distinct mass loss steps attributed to dehydration, dehydroxylation and decarbonation are observed for the indium containing hydrotalcite. Dehydration occurs over the temperature range ambient to 205 °C. Dehydroxylation takes place in a series of steps over the 238–277 °C temperature range. Decarbonation occurs between 763 and 795 °C. The dehydroxylation and decarbonation steps depend upon the Mg:In ratio. The formation of indium containing hydrotalcites and their thermal activation provides a method for the synthesis of indium oxide-based catalysts. 相似文献
11.
《Journal of solid state chemistry》2004,177(4-5):1382-1387
Combined mid-IR and Raman spectroscopies indicate that intercalation of hexacyanoferrate (II) and (III) in the interlayer space of a Zn,Al hydrotalcite dried at 60°C leads to layered solids where the intercalated species correspond to both hexacyanoferrate(II) and (III). This is an indication that depending on the oxidation state of the initial hexacyanoferrate, partial oxidation and reduction takes place upon intercalation. The symmetry of the intercalated hexacyanoferrate decreases from Oh existing in the free anions to D3d. The observation of a broad band around 2080 cm−1 is indicative of the removal of cyanide from the intercalation complex to the outside surface of the crystals. Its position in the intercalation complex is probably filled by a hydroxyl group. 相似文献
12.
Sara J. Palmer Laure M. Grand Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2011,103(2):473-478
The aluminate hydrotalcites are proposed to have either of the following formulas: Mg4Al2(OH)12(CO3
2−)·xH2O or Mg4Al2(OH)12(CO3
2−, SO4
2−)·xH2O. A pure hydrotalcite phase forms when magnesium chloride and aluminate solutions are mixed at a 1:1 volumetric ratio at
pH 14. The synthesis of the aluminate hydrotalcites using seawater results in the formation of an impurity phase bayerite.
Two decomposition steps have been identified for the aluminate hydrotalcites: (1) removal of interlayer water (230 °C) and
(2) simultaneous dehydroxylation and decarbonation (330 °C). The dehydration of bayerite was observed at 250 °C. X-ray diffraction
techniques determined that the synthesis of aluminate hydrotalcite with seawater and a volumetric ratio of 4.5 results in
very disordered structures. This was shown by a reduction in the mass loss associated with the removal of interlayer water
due to the reduction of interlayer sites caused by the misalignment of the metal-hydroxyl layers. 相似文献
13.
Vágvölgyi V Palmer SJ Kristóf J Frost RL Horváth E 《Journal of colloid and interface science》2008,318(2):302-308
The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were characterised by XRD, simultaneous TG-DTG-DTA and controlled rate thermal analysis (CRTA) to determine the stability and thermal decomposition pathway of the synthesised hydrotalcites. For the carbonate intercalated hydrotalcite dehydration takes place in three steps two of which are quasi-isothermal and one non-isothermal. Dehydroxylation and decarbonation occur separately over the 235-330 and 330-370 degrees C temperature range. A second non-isothermal decarbonation step is observed in the 371-541 degrees C range. In comparison the mixed carbonate-vanadate and carbonate-molybdate hydrotalcites show two dehydration steps and the dehydroxylation and decarbonation occur simultaneously. The observation of three dehydration steps is used to support the model of water molecules in three structurally distinct environments in the hydrotalcite interlayer. CRTA technology provides a mechanism for the decomposition of hydrotalcites. 相似文献
14.
Laure-Marie Grand Sara J. Palmer Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2010,101(1):195-198
Hydrotalcites based upon gallium as a replacement for aluminium in hydrotalcite over a Mg/Al ratio of 2:1 to 4:1 were synthesised. The d(003) spacing varied from 7.83 Å for the 2:1 hydrotalcite to 8.15 Å for the 3:1 gallium containing hydrotalcite. A comparison is made with the Mg/Al hydrotalcite in which the d(003) spacing for the Mg/Al hydrotalcite varied from 7.62 Å for the 2:1 Mg hydrotalcite to 7.98 Å for the 4:1 hydrotalcite. The thermal stability of the gallium containing hydrotalcite was determined using thermogravimetric analysis. Four mass loss steps at 77, 263–280, 485 and 828 °C with mass losses of 10.23, 21.55, 5.20 and 7.58% are attributed to dehydration, dehydroxylation and decarbonation. The thermal stability of the gallium containing hydrotalcite is slightly less than the aluminium hydrotalcite. 相似文献
15.
P. Kustrowski A. Wegrzyn L. Chmielarz A. Bronkowska A. Rafalska-Lasocha R. Dziembaj 《Journal of Thermal Analysis and Calorimetry》2004,77(1):243-251
Thermal decomposition of magnesium-aluminum hydrotalcites intercalated with four different polyoxometalate anions (V10O28
6−,Cr2O7
2−, W7O24
6−or Mo7O24
6−) was examined. The studied samples were prepared by the ion-exchange procedure starting from the parent carbonate-containing
hydrotalcite. The successful synthesis was confirmed by powder X-ray diffraction and chemical analysis. The samples decomposed
in two or three essential steps forming finally mixed metal oxides. The dichromate-containing hydrotalcite showed a thermal
reduction of Cr6+ to Cr3+ ions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
S. R. Naidu N. M. Bhide K. V. Prabhakaran E. M. Kurian 《Journal of Thermal Analysis and Calorimetry》1995,44(6):1449-1462
Nitroaminoguanidine (NAG) has been investigated as regards its thermal decomposition characteristics using simultaneous thermal analysis, infrared spectroscopy, X-ray diffraction and polarising microscopy. XRD studies show thatNAG crystal belongs to the tetragonal system. The crystal structure parameters are found to be:a=17.063±0.005Å,b=17.063±0.005Å,c=5.155±0.005Å andc/a axial ratio=0.302. Under non-isothermal conditions,NAG decomposed apparently in one stage with a loss in weight of 80%. But the thermal decomposition ofNAG in the solid phase under isothermal conditions proceeded through three stages. Both the first and the second stages obeyed theA-E (Avrami Erofee'v) equation forn=1. The 3rd stage is too slow and kinetics has not been attempted. The rate parameters for the first and second stages have been evaluated. Gaseous decomposition products detected using the IR gas cell are NH3, NO2, HCN, N2O, CO and CO2. High temperature IR studies indicate preferential deamination reaction initially indicating breaking of N?NH2 and C?NH2 bonds leading to NH2 radical formation. Addition of diphenylamine, a known chain inhibitor, decelerated the thermal decomposition, supporting a radical chain reaction. 相似文献
17.
Mg-Al-CO_3与Zn-Al-CO_3水滑石热稳定性差异的研究 总被引:6,自引:0,他引:6
层状双金属氢氧化物( Layered double hydroxides,简称 LDHs)是一类近年来发展迅速的阴离子型粘土,又称水滑石,其组成通式为: [M? 1-xM? x(OH)2]x+ Ax/nn-mH2O,其中 M?是二价金属离子, M?是三价金属离子, An-是阴离子。这种材料是由相互平行的层板组成,层板带有永久正电荷;层间具有可交换的阴离子以维持电荷平衡。通过离子交换可在层间嵌入不同的基团,制备许多功能材料,被广泛用作催化剂、吸附剂及油田化学品等,已引起人们的关 注 [1~ 4]。有关 Mg-Al-CO3与 Zn-Al-CO3水滑石的合成及性能研究国内外已有大量报道 [1… 相似文献
18.
Nidhuban Deb 《Journal of Thermal Analysis and Calorimetry》2013,111(1):491-498
Two heterobimetallic oxalate coordination compounds, zinc(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate (ZnOLa) and cadmium(II)heptaaquatris(oxalato)lanthanate(III)tetrahydrate (CdOLa) were synthesized and characterized by elemental analysis, IR, electronic spectral and powder X-ray diffraction studies. Both the compounds were found to have monoclinic structure. Thermal decomposition studies by TG, DTG and DTA in air have proved that the aqua ligands are associated with metals in a stronger coordination mode. The temperatures for pyrolysis were adopted from the TG results chosen from the stable range of thermograms. In case of ZnOLa, it decomposes through two steps and the end product at 1000 °C was found to be consisting of mainly, La2O3, ZnO and La2ZnO x through the intermediate formation of several oxycarbonates of lanthanum at ca. 525 °C. In case of cadmium analogue, three steps decomposition were observed and the final products were confirmed as CdO2, La2O3, LaCO and La2CdO x via the formation of several intermediates at 340 and 590 °C. The La2C3 and carbon are also found as part of the end product. The kinetic parameters, E *, lnk o, ?H # and ?S # of all the deaquated and decomposition steps are investigated and discussed from the DSC study in nitrogen. 相似文献
19.
Frederick L. Theiss Sara J. Palmer Godwin A. Ayoko Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1123-1128
The removal of the sulfate anion from water using synthetic hydrotalcite (Mg/Al LDH) was investigated using powder X-ray diffraction
(XRD) and thermogravimetric analysis (TG). Synthetic hydrotalcite Mg6Al2(OH)16(CO3)·4H2O was prepared by the co-precipitation method from aluminum and magnesium chloride salts. The synthetic hydrotalcite was thermally
activated to a maximum temperature of 380 °C. Samples of thermally activated hydrotalcite where then treated with aliquots
of 1000 ppm sulfate solution. The resulting products where dried and characterized by XRD and TG. Powder XRD revealed that
hydrotalcite had been successfully prepared and that the product obtained after treatment with sulfate solution also conformed
well to the reference pattern of hydrotalcite. The d(003) spacing of all samples was found to be within the acceptable region for a LDH structure. TG revealed all products underwent
a similar decomposition to that of hydrotalcite. It was possible to propose a reasonable mechanism for the thermal decomposition
of a sulfate containing Mg/Al LDH. The similarities in the results may indicate that the reformed hydrotalcite may contain
carbonate anion as well as sulfate. Further investigation is required to confirm this. 相似文献
20.
R. L. Frost J. M. Bouzaid A. W. Musumeci J. T. Kloprogge W. N. Martens 《Journal of Thermal Analysis and Calorimetry》2006,86(2):437-441
The thermal
stability and thermal decomposition pathways for synthetic iowaite have been
determined using thermogravimetry in conjunction with evolved gas mass spectrometry.
Chemical analysis showed the formula of the synthesised iowaite to be Mg6.27Fe1.73(Cl)1.07(OH)16(CO3)0.336.1H2O
and X-ray diffraction confirms the layered structure. Dehydration of the iowaite
occurred at 35 and 79°C. Dehydroxylation occurred at 254 and 291°C.
Both steps were associated with the loss of CO2. Hydrogen
chloride gas was evolved in two steps at 368 and 434°C. The products of
the thermal decomposition were MgO and a spinel MgFe2O4.
Experimentally it was found to be difficult to eliminate CO2
from inclusion in the interlayer during the synthesis of the iowaite compound
and in this way the synthesised iowaite resembled the natural mineral. 相似文献